Light and Immune Regulation: Why Photobiomodulation Does Not Simply “Switch Off” Inflammation

Red and near-infrared light are often described as having anti-inflammatory effects. It is a convenient explanation, but it can also be misleading, because inflammation is not a single substance, a single enzyme or one biological switch that can simply be moved into the OFF position.

Inflammation is an organised biological response. It can form part of the body’s defence against injury or infection, help recruit immune cells to the site of a problem, contribute to the removal of damaged structures and initiate processes that prepare tissue for repair. Once that role has been fulfilled, however, the character of the response must change so that repair can continue and the tissue can move back towards homeostasis.

The problem, therefore, is not the mere existence of inflammation. The problem arises when the response becomes too strong, lasts too long, occurs at the wrong time, or fails to transition appropriately from defence towards repair. This is exactly where photobiomodulation becomes biologically interesting — not as an inflammation switch, but as a signal capable of altering the regulatory environment of cells and the immune system.

Recent scientific reviews describe effects of PBM on mitochondrial and redox signalling, cytokines, macrophages, T lymphocytes, dendritic cells and a wide range of regulatory pathways involved in inflammation and tissue repair. A large proportion of these mechanistic findings, however, still comes from cellular and animal models. That distinction matters, because biological plausibility is not automatically clinical evidence.

Inflammation Is Not the Enemy

Imagine damaged tissue. Injured cells release signals, local blood vessels change their activity, immune cells move into the area and cytokines and other mediators are released. Some damaged cells and structures must be removed, and repair begins.

All of this can be part of a normal inflammatory response. If we blocked it completely, we would not necessarily help the organism. On the contrary, we could interfere with processes that are required to deal with the damage and subsequently rebuild the tissue.

A good biological outcome is therefore often not as little inflammation as possible, but rather an appropriate inflammatory response at the appropriate time, followed by the ability to resolve that response and restore the tissue.

That distinction is fundamental.

The Immune System Does Not Work Like a Thermostat with One Dial

When we say “immunity”, it is easy to imagine a single force that can be increased, reduced or “boosted”. The real immune system is far more complex. It consists of many types of cells, signalling molecules and regulatory mechanisms whose behaviour changes according to tissue type, the nature of the injury, the phase of the biological response, the local metabolic environment, the presence of microorganisms, neural and hormonal signals, age, and the person’s health and functional state.

That is why it is problematic to say that red light therapy simply “boosts immunity”. It is equally imprecise to claim that it “suppresses immunity”.

A more accurate word is:

MODULATES

This means that PBM may alter how certain cellular and molecular processes behave within a particular biological context.

Light Does Not Begin with a Cytokine. It Begins with the Cell.

Photobiomodulation does not work by allowing a photon to find an IL-6 or TNF-α molecule and simply “switch it off”. The primary interaction takes place at the level of cells and molecular structures capable of absorbing or mediating the optical signal.

One of the most extensively studied mechanistic frameworks involves mitochondrial and redox signalling. Downstream changes may involve redox state, reactive oxygen species, nitric oxide, membrane potential, calcium signalling, energy metabolism and transcription-factor activity. Only after these upstream events may changes in gene expression, cytokine production and cellular behaviour emerge.

Contemporary mechanistic reviews of PBM discuss pathways such as NF-κB, Nrf2, PI3K/Akt, MAPK/ERK, mTOR, JAK/STAT and other regulatory systems. The exact result, however, depends on the tissue, the state of the cell, the dose and the wider biological context.

This means that light does not necessarily “treat inflammation” directly. It may instead change the conditions in which the cell determines how to respond to an inflammatory stimulus.

ROS Are Not Simply Damage

Reactive oxygen species — ROS — have a poor reputation in everyday health communication. They are associated with oxidative stress, damage, ageing and inflammation, and all of those associations can be valid when ROS production is excessive or prolonged.

A small, short-lived and precisely localised increase in ROS can have a very different role. It can function as a signal through which the cell recognises that its environment has changed. Such a redox impulse may activate adaptive pathways and alter gene expression.

Under certain conditions, PBM may create exactly this kind of transient shift in redox signalling. Mechanisms such as Nrf2 may then become involved in antioxidant and cytoprotective responses, while NF-κB remains one of the major regulators of inflammatory signalling.

It is therefore biologically inaccurate to think of red light therapy as an “antioxidant made of light”. A more accurate model is:

light → controlled cellular signal → regulatory response

Cytokines Are Not “Good” or “Bad”

IL-1β, IL-6, TNF-α, IL-10 and TGF-β are often given simple labels in articles about inflammation: pro-inflammatory equals bad, anti-inflammatory equals good. Biology is far less binary.

Cytokines are information molecules. Their meaning depends on amount, timing, location, the cells producing them, the cells receiving them and the phase of the organism’s response. A short-term increase in a particular inflammatory cytokine may be a necessary part of defence or repair. The problem may arise only when its activity becomes excessive, chronic or poorly regulated.

PBM research shows that light stimulation can, in some models, alter the expression and release of cytokines and growth factors. The results, however, differ across cellular models, doses and optical parameters.

For TANVEA, this leads to a fundamental principle:

The goal is not to reduce inflammatory cytokines as much as possible. The goal of the biological system is to regulate the inflammatory response appropriately.

Macrophages: Cells Between Defence, Clearance and Repair

One of the most interesting areas of PBM research involves macrophages. These are highly plastic cells of the innate immune system capable of recognising injury, engulfing cellular debris and microorganisms, producing cytokines, communicating with other immune cells, influencing the formation of new blood vessels, regulating extracellular-matrix repair and participating in the resolution of inflammatory responses.

Older models often divided macrophages into two major groups: M1, described as pro-inflammatory, and M2, described as anti-inflammatory or regenerative. This model is useful for teaching, but it is not fully accurate.

Modern immunology shows that macrophages do not exist only in two clearly separated states. In real human tissue, they occupy a continuum of highly plastic functional states that change according to the surrounding environment. The terms M1-like and M2-like are therefore more accurate than the idea of two rigid cell types.

It is precisely this plasticity that makes PBM biologically interesting.

Can Light Change Macrophage Behaviour?

Research suggests that it can. A review published in 2025 analysed 19 experimental studies focused directly on PBM and macrophage polarisation or functional state. Across several models, changes were observed away from strongly pro-inflammatory profiles and towards states associated with inflammatory resolution and tissue repair.

Mechanisms investigated included NF-κB, PI3K/Akt/mTOR, STAT signalling, cellular metabolism, mitochondrial activity and redox state. The authors also highlighted substantial variation in the wavelengths, doses and biological models used across the studies.

The simple statement that “red light converts M1 macrophages into M2 macrophages” would therefore be a major oversimplification.

A more accurate formulation is:

Under certain biological conditions, PBM may influence macrophage functional state and support a shift in the inflammatory environment towards processes associated with resolution and repair.

That is much closer to biological reality.

Why We Do Not Want “As Many M2 Macrophages as Possible”

This is where the danger of simplistic marketing becomes particularly clear. If we accepted the equation “M1 = bad” and “M2 = good”, we could reach the absurd conclusion that the more M2 macrophages we have, the better.

That is not true either.

M2-like profiles can be useful during healing and inflammatory resolution, but in other biological contexts certain M2-like programmes may contribute to fibrotic processes or help create an environment that is not desirable. This is one of the reasons the scientific literature emphasises that the simple M1/M2 dichotomy does not reflect the true complexity of macrophage biology.

The biological objective is therefore not to create one “good” type of immune cell. It is to allow the immune system to move dynamically between functional states according to what the tissue actually requires.

The Immune System Is More Than Macrophages

Recent comprehensive reviews of PBM-mediated immunomodulation extend far beyond macrophages. They also describe potential effects on T lymphocytes, dendritic cells, cytokine networks and broader cellular signalling.

Dendritic cells play a central role in transferring information between innate and adaptive immunity. T lymphocytes are essential for targeted immune responses and their regulation. This opens a much broader perspective: photobiomodulation may not be merely a local “anti-inflammatory intervention”, but may influence communication between different layers of the immune response.

Scientific discipline is essential here. For many of these mechanisms, we have compelling cellular and animal data but fewer high-quality human clinical studies.

It is therefore appropriate to say:

“PBM may modulate immune mechanisms.”

Not:

“PBM repairs the immune system.”

Inflammation Has a Temporal Architecture

One of the most important ideas in this entire subject is time. An inflammatory response has a trajectory.

In a highly simplified form, we can think in terms of the following phases:

1. DETECTION AND DEFENCE
   The organism identifies injury or threat.

↓

2. INFLAMMATORY ACTIVATION
   Cells and mediators required to manage the situation become activated.

↓

3. DAMAGE CLEARANCE
   The immune system removes damaged cells, material and, depending on context, pathogens.

↓

4. RESOLUTION
   The character of the inflammatory environment changes actively.

↓

5. REPAIR AND REMODELLING
   The tissue repairs itself and moves back towards functional balance.

This process is not merely the passive “fading away” of inflammation. Resolution of inflammation is an active biological process.

That distinction is important when interpreting PBM. If light stimulation helps alter the cellular and regulatory environment in a way that allows the system to move from a prolonged inflammatory state towards repair, its value may not lie in simply suppressing one cytokine.

It may lie in:

changing the trajectory of the biological response.

Light Cannot Be Separated from the State of the Tissue

Imagine two biologically different situations. In the first, we have healthy tissue after a short-term physiological load. In the second, chronically damaged tissue with a persistently altered redox and inflammatory environment.

Both receive the same optical stimulus.

Is it reasonable to expect exactly the same response?

No.

A cell interprets the signal according to its current biological state. Relevant variables may include mitochondrial function, redox environment, the presence of inflammatory mediators, metabolic state, perfusion, oxygen availability, extracellular-matrix state and the activity of neighbouring cells.

This is one reason why the same PBM protocol does not necessarily produce the same result in every person. It is also one reason why TANVEA Light Systems™ do not treat light as an isolated intervention.

Dose Matters in Immunomodulation Too

Light is not a drug in a tablet, where biological dose can be reduced to the amount of one active ingredient. With PBM, relevant variables include wavelength, spectral composition, irradiance, fluence, time, distance, treatment area, geometry, the optical properties of the tissue and frequency of repetition.

The same number of joules does not necessarily produce the same biological response if that energy is delivered in a different way. Recent scientific reviews highlight substantial heterogeneity in the parameters used in PBM immunomodulation studies.

That matters enormously. If one study demonstrates a cytokine change with a particular wavelength and dose, we cannot conclude that “all red light reduces inflammation”. Such a conclusion would skip a large part of both the physics and the biology.

This is precisely why TANVEA Light Systems™ do not view light technology merely as a source of a certain number of watts or LEDs. A biologically relevant light system must consider which spectrum, what irradiance and what spatial distribution of light actually reach the target tissue at a defined working distance.

Wavelength, power, geometry, distance and time are not isolated marketing specifications. Together they create the optical environment to which the biological system responds.

TANVEA therefore moves away from the question:

“How powerful is the source?”

towards the more precise question:

“What biologically relevant optical stimulus does this system create at the human body?”

Why We Cannot Infer a Clinical Outcome from a Cellular Mechanism Alone

Imagine a laboratory study in which cells produce less IL-6 after PBM. That finding is interesting, but there is a very long journey from that observation to a real person.

We still need to know whether a comparable dose reaches the target tissue, whether human cells respond in the same way, whether the cytokine change is large enough, whether it is clinically meaningful, whether it lasts long enough, whether it improves pain, function or healing, and whether the finding holds in a specific diagnosis.

This is why TANVEA distinguishes between:

MECHANISTIC EVIDENCE

and

CLINICAL EVIDENCE

Mechanism helps explain the possible why.

Clinical research must demonstrate the real-world what.

That distinction is fundamental to responsible scientific communication about PBM.

What Do We Already Know Clinically?

PBM is no longer merely a laboratory experiment.

An umbrella review published in 2025 included 15 meta-analyses, 204 randomised clinical trials and more than 9,000 participants across 35 assessed outcomes and 15 health conditions. Evidence was favourable for some outcomes. For many others, however, certainty remained low or very low because of protocol heterogeneity, small studies and other methodological limitations.

The authors therefore emphasised the need for higher-quality trials and better standardisation of PBM protocols.

A separate international expert consensus published in 2025 already considers PBM clinically relevant for several specific indications. Even this consensus, however, does not describe PBM as a universal “immunotherapy”.

That is precisely the level of certainty we need to preserve.

“Anti-Inflammatory” Is Therefore True — but Only Partly

We can say that PBM has anti-inflammatory effects in many experimental and some clinical contexts. That statement is not incorrect, but it is incomplete.

Behind the term “anti-inflammatory” may lie several different processes: changes in redox signalling, modulation of NF-κB and other transcriptional pathways, changes in the cytokine environment, changes in macrophage behaviour, modulation of cellular metabolism and support for the transition from an inflammatory phase towards tissue repair.

For TANVEA, it is therefore more accurate to speak of:

IMMUNOMODULATION

rather than simply:

INFLAMMATION SUPPRESSION

Red Light Does Not “Boost Immunity”. It Gives Cells a Signal.

The statement “red light therapy boosts the immune system” sounds attractive, but biologically it is too simplistic.

A stronger immune system is not always a better immune system. Excessive immune activation can damage the body’s own tissues. Insufficient immunity can fail to defend the organism. Chronically active immunity can sustain inflammation.

A well-functioning immune system therefore does not need to be as strong as possible. It needs to be appropriate, adaptive and well regulated.

That is much closer to what current science allows us to say about the biological potential of photobiomodulation.

TANVEA Model: SIGNAL → STATE → RESPONSE

For Light Systems™, this entire subject can be summarised using a simple biological framework.

SIGNAL

Light enters the tissue and creates a physical stimulus.

↓

STATE

The cell receives that stimulus in a particular biological state. This state may include mitochondrial function, redox environment, metabolic conditions, oxygen availability, the inflammatory environment and the state of the surrounding tissue.

↓

RESPONSE

The interaction between the incoming signal and the current biological state produces a biological response.

That response may then appear across several interconnected levels:

Regulatory network
→ NF-κB, Nrf2, PI3K/Akt, MAPK, STAT and other signalling pathways

↓

Immune behaviour
→ changes in the cytokine environment and in the behaviour of macrophages and other immune cells

↓

Tissue response
→ changes in the conditions governing inflammation, repair, healing and remodelling

This model is never perfectly linear. Feedback exists between the individual levels, and the outcome is influenced not only by light itself, but also by the state of the person and the biological context of the tissue.

Therefore:

Photobiomodulation is not a command given to a cell. It is a biological input entering an already existing regulatory system.

And This Is Why PBM Does Not Have One Universal “Anti-Inflammatory Effect”

If red light always and under all circumstances simply suppressed inflammation, its biological value would paradoxically be smaller.

The immune system sometimes needs inflammation. After acute injury, it must respond. During infection, it must create a defensive environment. During healing, it must remove damaged material. Only then does it need to resolve the inflammatory process.

A biologically intelligent response is therefore not always the same.

It is context-dependent.

This is why one of the most important questions for future PBM research will not simply be whether light alters inflammation, but at what stage, in what tissue state, at what dose and in which direction.

Where the Boundaries of Knowledge Are Today

Research into PBM-mediated immunomodulation is highly active. We now have extensive mechanistic literature, cellular studies, animal models, a growing number of human clinical studies, systematic reviews and clinical consensus statements for selected indications.

What we still do not have is a universal answer to questions such as:

What is the ideal dose “for immunity”?
Such a universal dose probably does not exist.

Which wavelength is best for inflammation?
Without defining the target tissue, biological problem and intended outcome, the question is too broad.

Can light be used to treat autoimmune disease?
Current evidence does not justify such a general claim.

Can a whole-body panel “boost immunity”?
Current evidence does not support that as a universal statement.

These are not weaknesses of photobiomodulation.

They are boundaries of current knowledge.

And respecting boundaries is part of good science.

The TANVEA Perspective: Inflammation Is Not the Problem. Loss of Regulation Is.

From the TANVEA perspective, this is the most important idea in the entire article.

Inflammation is not automatically the enemy. ROS are not automatically the enemy. Cytokines are not automatically the enemy. Immune activation itself is not automatically the enemy.

All of these processes have a place in a properly functioning organism.

What matters is intensity, timing, location, context and the ability of the system to move into the next phase.

That is why we do not view photobiomodulation as light whose purpose is to “stop inflammation”. We view it as one possible biological signal entering the regulatory network of the organism.

Its value may not lie in suppressing the response. It may lie in helping create conditions in which the response can develop appropriately, come to an end and transition towards repair.

And that is a much deeper meaning of the word:

REGENERATION

What to Take Away from This Article

Photobiomodulation is not a simple anti-inflammatory switch.

Research suggests that red and near-infrared light may influence mitochondrial and redox signalling, regulatory pathways such as NF-κB and Nrf2, cytokine production, macrophage behaviour and other cells of innate and adaptive immunity.

Macrophage research in particular provides a growing body of preclinical evidence indicating changes in functional state towards environments associated with inflammatory resolution and repair.

This does not mean that PBM “switches off inflammation”, “boosts immunity” or “treats inflammatory diseases” in general.

The biological outcome depends on tissue, biological context, the phase of the inflammatory response, spectral composition, dose, geometry and the state of the individual.

The most accurate formulation is therefore:

the immunomodulatory potential of photobiomodulation.

Light is not a command.

It is a signal.

And its meaning is determined by the biological system that receives it.

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FAQ

Does red light have an anti-inflammatory effect?

Yes, but PBM does not simply “switch inflammation off”. In many experimental and some clinical models, it may alter redox signalling, the cytokine environment and immune-cell behaviour. It is therefore more accurate to speak of modulation of the inflammatory response.

Does red light therapy boost the immune system?

It is not accurate to describe PBM as simply “boosting immunity”. The immune system needs appropriate regulation, not maximum activation. PBM may influence some immune mechanisms, but it is not a universal immune stimulant.

What are macrophages?

Macrophages are cells of the innate immune system involved in defence, removal of damaged material, regulation of inflammation and tissue repair. They are highly plastic and change their behaviour according to the biological environment.

Does red light convert M1 macrophages into M2 macrophages?

It is not accurate to describe the process as a simple M1 → M2 switch. M1/M2 is a simplified model. Research suggests that PBM may influence macrophage polarisation and functional state, but real macrophages exist across a wide spectrum of phenotypes.

Does PBM reduce cytokines such as IL-6 or TNF-α?

Reductions in these mediators have been observed in some experimental models, but the effect is not universal. It depends on tissue, biological model, phase of the response and optical parameters.

Are ROS always harmful?

No. Short-lived and controlled changes in ROS are an important part of cellular signalling and adaptation. Excessive or chronic production is the greater concern.

Can red light therapy be used in autoimmune disease?

General mechanistic findings cannot be turned into a universal recommendation for autoimmune diseases. These are complex medical conditions, and any intervention must be considered individually and in relation to the specific diagnosis.

Does higher panel output mean a stronger anti-inflammatory effect?

No. Higher output does not automatically produce a stronger or better biological response. PBM depends on spectrum, irradiance, dose, geometry, time, distance, tissue and the biological state of the individual.

Is the immunomodulatory effect of PBM clinically proven?

---

Mechanistic and preclinical evidence is extensive, and high-quality human clinical data exist for some specific indications. There is not, however, a universally clinically proven “immunomodulatory protocol” applicable to every disease or every person.

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SCIENTIFIC REFERENCES

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TANVEA EDITORIAL NOTE

This article is intended for professional education and to explain the current state of scientific knowledge.

Terms such as “anti-inflammatory effect” or “immunomodulation” do not mean that photobiomodulation is a universal treatment for inflammatory, infectious or autoimmune diseases.

The biological response depends on the diagnosis, the tissue, the optical parameters and the individual health context.